A patent literature 1 exemplifies a conventional motor drive.
FIG. 7 shows a circuit block diagram thereof. In FIG. 7, 1 denotes a three-phase alternating current power supply, 2 denotes a three-phase diode bridge rectifying circuit, 3 denotes a buck chopper portion having a switching element 3a, a reactor 3b, and a diode 3c, 4 denotes a voltage source three-phase full-bridge inverter portion for supplying a three-phase power to an alternating current motor (PM motor) 5 by a switching action thereof, 6 denotes a regenerative power bypass diode connected in an anti-parallel connection to buck chopper portion 3, 7 denotes an inverter portion control circuit configured to output a switching command to inverter portion 4 in order for a power factor of alternating current motor 5 to be approximately 1, 8 denotes a small-capacitance capacitor installed between output terminals of buck chopper portion 3, 9 denotes a starter circuit, and 39 denotes a smoothing electrolyte capacitor. Inverter portion control circuit 7 includes: a resistance voltage division circuit 7a configured to detect a phase voltage of alternating current motor 5; an integrator 7b which inputs the phase voltage of alternating current motor 5; a capacitor 7c configured to determine a positive or minus of an output of integrator 7b; a photo-coupler 7d which inputs a determination result of comparator 7c; and a logic circuit 7e configured to output a switching command with a signal from photo-coupler 7d as input thereof.
In logic circuit 7e, the switching command is outputted to inverter portion 4 in order for the phase voltage and the phase current to become the mutually same phase.
It should be noted that integrator 7b eliminates noises included in a voltage waveform.
A chopper control circuit to perform a switching of switching element 3a calculates a difference between the switching command value and a current flowing in a reactor 3b through a subtractor 3d and the calculation result is inputted to a PI control portion 3e. Comparator 3f performs a comparison of a magnitude between a reference signal having a predetermined frequency and the output signal of PI control portion 3e and supplies a comparison result signal to switching element 3a as a switching command. Consequently, the flow of an over-current across alternating current motor 5 can be suppressed.
In the motor drive in FIG. 7 described in Patent Literature 1, buck chopper portion 3 is incorporated into an input side of inverter portion 4, regeneration power bypassing diode 6 is connected in anti-parallel connection with respect to buck chopper portion 3, inverter portion 4 is, furthermore, structured in a 120-degree conduction inverter and is controlled as a pseudo current source inverter and both characteristics of the current source inverter and the voltage source inverter can be obtained. In addition, the power factor of alternating current motor 5 is set approximately to 1. Hence, a conduction interval of time of regenerative power bypassing diode 6 can be shortened and can become near to the waveform of the inverter portion can become near to the waveform of the current source inverter. In addition, higher harmonic components can be reduced, a voltage waveform thereof can become near to a sinusoidal waveform, and high efficiency and low noise motor drive can be achieved.
On the other hand, non-patent literature 1 extends the method described in Patent literature 1 to a vehicle mounted electric driven assistance turbocharger inverter, specializing in the buck chopper (pseudo current source inverter) and in a sensor-less drive. A function to boost the voltage from battery voltage of 12 volts is not yet discussed and the circuit structure is a direct current power supply of 72 volts as a premise.    [Patent Literature 1] A Japanese Patent No. 32 78 188    [Non-patent literature 1] Toshihiko Noguchi (Nagaoka University of Technology) titled Performance of Mechanical-Sensorless Operation of Pseudo Current-Source Inverter Fed Ultra High-Speed PM motor